1. Field of the Invention
The present invention relates to apparatus for use with endoscopic medical video equipment. More particularly, this invention pertains to an endoscopic adapter including a zoom lens.
2. Description of the Prior Art
The advent of various endoscopic instruments has proven to be a significant aid to diagnosis and to surgical procedures. Such instruments generally include an elongated probe for penetration and viewing of otherwise inaccessible body regions. The physician is able to view the body region adjacent to the distal end of the probe through an eyepiece near the proximal end. Examples of endoscopic instruments include the laparoscope, cystoscope, arthroscope, bronchoscope, colonoscope, etc. the functions and areas of use of which are apparent from the nomenclature.
While providing a substantial technical advance, the utility of the endoscope has been significantly increased by the development of video cameras for coupling to the image output of the endoscope. The use of such a camera protects the vision of the physician in those instances in which a highly-reflective medium must be viewed with bright illumination. This often occurs in arthoscopic surgery where high intensity illumination of reflective articular tissue can cause injury to the retina of an operating physician.
The combination of video camera with the endoscope, as opposed to direct viewing, promotes the operator comfort and, hence, instrument utility. When using a camera, the physician needn't position himself throughout the examination to accommodate an eyepiece located near the proximal end of the endoscope. An assistant may hold and position the endoscope while the operating physician's hands are freed to manipulate the surgical tools. As the physician and his assistant may view the image at the same time on a common monitor, prompt and accurate movement of the scope is assured throughout the operation. Thus tissue trauma due to movements of the scope is lessened.
Finally, the incorporation of a video camera permits both recordation and real time transmission of procedures. This opens many possibilities not offered by conventional endoscopy including real time consultations (and teaching) from distant venues and significant documentation benefits.
The adaptation of video camera technology to endoscopic imaging requires a means for adapting the conventional endoscope to a video camera head. Conventional apparatus for this purpose includes a mechanism for grasping the endoscope that is, in turn, coupled at its opposed end to the camera head. (Fixed focal length optics, within the adapter, transmit a circular image of the proximal end of the endoscope to the camera head for viewing on a monitor.) Means are provided in association with the adapter for focusing the image.
The size of the image of the proximal end of an endoscope is a function of probe diameter. Probes may vary in diameter from less than two (2) millimeters to approximately twelve (12) millimeters. For example, arthroscopic joint surgery generally requires an approximately four (4) millimeter diameter probe while twelve (12) millimeter probes are utilized for laparoscopy (abdominal cavity surgery).
Viewing clarity is, of course, essential to the physician. Generally the image should occupy approximately eighty (80) per cent of the height of the screen of a standard monitor to provide sufficient detail. Unfortunately, the fixed focal length optics of the conventional adapter cannot adjust image size to compensate for the different endoscopic procedures (and correspondingly different sized probes) the physician may desire to perform.
Diagnosing and operating physicians work most advantageously with little variation of image sizes. As a result, the physician has been required to maintain a number of adapters of different fixed focal lengths to compensate the image sizes produced by the probes utilized in different procedures. Such adapters are relatively expensive optical instruments. A "complete" set (by today's standards) covers a range of 25 to 40 millimeters (3 to 4 millimeter increments). Due to the expense, a physician typically purchases three adapters (25, 32 and 38 millimeter focal lengths). This represents a rough compromise between cost and viewing convenience.
Since an endoscope is employed within a critical environment, the entire system must be disinfected before use. Prior to use the components are generally immersed in a disinfecting bath for about fifteen minutes, then dried and assembled for use. The presence of even minute residual amounts of condensation on the front lens of the adapter can significantly effect viewing clarity.
Some procedures may require a change in magnification during use to permit closer viewing of the critical site. Such a substitution, of course, multiplies the chance that the physician's view will be hampered by condensation induced problems. Resulting delays can significantly hinder both diagnoses and surgical procedures.